The present invention relates to heat pumps and, in particular, the management of refrigerant charge in heat pumps.
Heat pumps provide thermal energy from a heat source to a heat sink, moving thermal energy opposite to the direction it would normally flow. Heat pumps can be used to provide indoor cooling, for example, expelling heat from an indoor area into an outdoor environment. Heat pumps can also be used to heat a water supply, drawing heat from the outdoor or indoor environments. Heat pumps often offer lower heating costs, air conditioning costs, and hot water preparation costs among existing technologies, and are gaining increased acceptance in the marketplace.
Heat pumps may include two or more modes of operation. For example, a heat pump might operate in a space cooling mode and may operate in a water heating mode. An appropriate amount of refrigerant charge in one mode may be insufficient for the amount of refrigerant needed in another mode. For example, liquid refrigerant can accumulate in a space cooling heat exchanger, reducing the liquid refrigerant otherwise available for water heating.
Excess refrigerant during transient operation or periods of low evaporator heat load can be stored in an accumulator upstream of a compressor. An accumulator can prevent damage to the compressor caused by liquid compression and oil dilution. However, it remains desirable to improve the management of refrigerant charge for heat pumps, and in particular heat pumps having multiple modes of operation.